Matched-field inversion for source location, environmental properties, or
a combination of the two (focalization) is based on comparing measured acoustic
fields to replica fields predicted for a variety of possible environmental
parameters and/or source positions using a numerical propagation model.
Although this approach is conceptually straightforward and widely applicable,
it requires a large number of replica-field computations and can be
impractically slow if the propagation modeling is not carried out in an
efficient manner. This is particularly true for environmental inversion and
focalization where the expanded parameter search space generally requires a
very large number of replica field computations, even if a relatively efficient
optimization algorithm such as simulated annealing (SA) is employed. This paper
describes matched-field inversion for geoacoustic properties using SA and rapid
acoustic-field modeling. The replica-field modeling is based on the normal mode
solution and makes use of multivariate interpolation of precomputed ``look-up''
tables of modal quantities stored as a function of the geoacoustic parameters.
The optimum grid-element size for the modal tables is considered, and two
interpolation schemes, linear and Shepard's method (locally quadratic), are
investigated. An example is given of geoacoustic inversion in a North Pacific
environment.